Communications between the engine controller of a motor vehicle and off-board devices are becoming more standardised. This is mainly due to the development of OBD II legislation in California, which has been propagated across the US and Europe and is now being taken on by many other countries. The legislation requires the support of certain standard communications protocols and also the provision of certain standard pieces of data by those protocols. This is intended to allow the vehicle service industry access to information from sensors and actuators on the vehicle such they can make effective and efficient repairs to vehicles. This information can also be accessed by any other monitoring device that might be fitted to the vehicle, and is not restricted to dealer service tools.
However, across the entire fleet of vehicles with differing engine types and configurations, there are relatively few truly “common” pieces of information (eg common parameters exist for engine rpm and engine coolant temperature). Therefore, in practice, many of the parameters are available only as “manufacturer specific” items. This includes not just the parameter identifier (PID), but also any scaling information that might be required to decode it.